Your cervix is where your uterus (womb) opens into your vagina. The scan will look for early signs of the cervix opening before your baby is due. Cervical length scans may also be recommended if you are expecting twins, or have had surgery to your cervix.

Your cervix should stay closed throughout your pregnancy, until just before you give birth. The cervix has a plug of mucus in it (called a show), and if this comes away early, infection may get into your uterus. If your cervix starts to open too soon, sadly, there is a danger that your baby will be stillborn, or born extremely prematurely (before 24 weeks).

Experts aren’t sure if infection gets in because the cervix is not tightly closed, or whether the infection causes the cervix to open. Either way, treating the infection promptly is vital.

A cervical stitch may be put in before you are 16 weeks pregnant if your cervix is shortening or beginning to open. Though a stitch can be inserted later, if doctors are worried about the safety of your baby. The stitch prevents the cervix from opening further, and keeps the mucus plug in. You’ll only have a stitch if it is absolutely necessary, because, as with any surgical procedure, it increases the risk of infection.

A vaginal scan is the best way to clearly see and measure your cervix. The cervix looks like a tube on the scan, between 3cm (1.2in) and 5cm (2in) long, with one end at the top of the vagina (the external os), and the other end inside the uterus (the internal os).

It is the internal os that can begin to open first, and this will appear as a V-shape on the scan. As the os opens further, it becomes U-shaped (funneling). If the closed part of the cervix measures less than 2.5cm (1in), your surgeon will put in a stitch under a general anaesthetic. The stitch will be removed a few weeks before your due date.

When you have the scans depends on whether you have been pregnant before, and how those pregnancies fared. It may only be necessary to check at 16 weeks, 20 weeks and 24 weeks and, if your cervix is long and closed each time, no more scans will be needed. Sometimes, fortnightly scans are done during the second trimester, and vaginal swabs are also taken, to look for infection.

When normal labour starts, you will have painful contractions as your cervix opens. But if there is a risk that your cervix is weak, regular scans are important, because it could open without the usual signs of pain or bleeding.

Last reviewed: March 2013

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Comments

My cervix length is 28mm which got picked up later week (28weeks consultation). I had a cervical scan there and then. I have to go back in two weeks to have another scan, which I'm stressing about big time. This is my 6th baby and I have never had anything out of the ordinary with the other pregnancies, so this was a shock :-( I'm on bed rest which isn't easy when the husband is hardly there as he works long hours and the kids are running around. Praying to go to at least 37weeks :-) xxxx

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